This invention relates in particular to commercial kitchens, where holding ovens are used as distinguished from baking ovens. In order to hold foods in a warm condition, it is necessary to have control over the oven temperature, a normal holding temperature being 160.degree. to 200.degree. F. In practice, baking ovens operate up to and above 550.degree. F. with vents that continuously discharge burnt gas with a large proportion of heated air. The oven vent discharge is usually within a range of 500.degree. to 600.degree. F. during normal kitchen operations and is a source of heat greater than that required to maintain a holding oven temperature. Conventionally, this vent heat is simply waste heat. Therefore, it is a primary object of this invention to advantageously utilize the vent discharge heat source of a baking oven for convection heating the interior of a separate holding oven without resort to any other heat source, thereby usefully conserving heat.
Heretofore, baking and holding ovens of the type under consideration have been heated by conduction and by individual heat sources, electrical or gas; it being gas stoves and ovens with which this invention is particularly concerned. Gas stoves and ovens are temperature controlled by means of thermostats, a gas heated baking oven having gas burners for maintaining a temperature of for example 550.degree. F., and a gas heated holding oven having gas burners for maintaining a moderate temperature of approximately 200.degree. F. Heretofore, baking and holding ovens have been essentially the same in construction, and the latter being essentially the same and as costly as the former. Therefore, it is an object of this invention to reduce the cost of holding ovens by providing heat transfer by convection from a primary baking oven into a secondary holding oven. It is also an object of this invention to provide heat control whereby the holding oven temperature can be regulated as circumstances required. In practice, damper controls are provided.
Heretofore, secondary ovens have been subjected to flue heat of primary ovens so that flue heat is conducted through the secondary oven walls to heat the secondary oven chamber. However, such an arrangement is not altogether satisfactory, as a thermostat controlled oven turns the fire on and off with commensurate fluctuations in flue heat. Accordingly, it is an object of this invention to moderate any fluctuations in flue heat by providing a heat transfer wall between the primary and secondary ovens which limits a substantially constant heat transfer by conduction therebetween. In practice, the primary oven temperature remains substantially constant while the flue heat thereof will fluctuate. In carrying out this invention, the pan of the secondary oven is common to the roof of the primary oven, for limited heat transfer by conduction therethrough whereby the secondary oven temperature is held to a substantially constant reduced level. For example, the baking range of a typical primary oven is 250.degree. to 600.degree. F., in which case the limited heat transfer through the common pan-roof is 150.degree. to 200.degree. F. In accordance with this invention, the pan-roof heats ambient inlet air to said 150.degree. to 200.degree. F. range, to be supplemented by the forceful hot vent air from the primary oven, as circumstances require to adjust to the desired holding temperature.
The normal vent discharge temperature of a baking oven is in the range of 500.degree. to 550.degree. F., while the normal ambient air temperature in a kitchen is 75.degree. to 80.degree. F. It is to be understood that these temperature ranges vary from one kitchen to another. Accordingly, it is an object of this invention to temper ambient inlet air by conduction of primary oven heat through the aforesaid pan-roof for convection flow within the secondary oven chamber, and by proportionally commingling hot air therewith, namely with the primary oven vent air. In practice therefore, the primary baking oven vent is controlled by a damper that discharges into the secondary holding oven, there being an ambient air inlet into the holding oven tempered by the pan-roof and by the primary vent air. The upward flow of heated air is by means of convection in both instances, and in accordance with this invention it is an object to vent the secondary holding oven in such a way that the commingling of prinary oven vent air with secondary oven ambient inlet air is automatic. To this end, the secondary vent opening of the secondary holding oven is equal to or greater in area than the primary holding oven vent. And in order to reduce temperature to a holding range, the ambient inlet openings of fixed area are provided. In practice, with the oven doors closed, the discharge at the secondary holding oven vent cannot exceed, by convection, the inlet from either or both the primary oven vent and/or the ambient inlet. In this manner, complete control is achieved through the single primary oven vent damper, the excess primary vent air being discharged in a conventional manner at the rear of the primary baking oven.
A feature of this invention is that the constructions of the primary baking oven and the secondary holding oven can be conventional in most every respect, except as herinafter described. The requesites are, that the primary baking oven must provide an exhaust vent of hot air at or above the holding oven temperature desired, and that the secondary holding oven be placed above and preferably over the primary baking oven. In carrying out this invention, the primary baking oven is vented partially or completely through the secondary holding oven as circumstances required. By operating the primary oven at sufficiently high heat, the secondary oven can also be used for baking.